This site is operated by a business or businesses owned by Informa PLC and all copyright resides with them. Informa PLC's registered office is 5 Howick Place, London SW1P 1WG. Registered in England and Wales. Number 3099067.

As the numbers show in our recently compiled list of May's top-selling smartphones at AT&T, Verizon Wireless, Sprint and T-Mobile, the Samsung Galaxy S4 is a force to be reckoned with, particularly for its biggest rival, Apple's iconic iPhone.

Despite increasing the screen size of the iPhone for the first time last year – from 3.3 inches to four inches – Apple still gets a lot of criticism from industry watchers who say the Silicon Valley giant has to go bigger to better compete against larger devices, namely the Galaxy S4.

Well, that day could be coming. Citi Research, in a note to investors, has predicted that Apple will unveil a 4.8-inch iPhone 6 as soon as the first quarter of next year, CNET reported. That potentially would be just a few months after the presumed launch of the iPhone 5S, which is not expected to look drastically different from its 2012 predecessor, the iPhone 5. Fans of Apple's mobile products might have to be satisfied with the upgrades to iOS 7, at least for now.

Citi also said production of the 5S has been delayed a few weeks, but it should still make its appearance in September; there just might not be as many available to buy. The financial-services firm's predictions are based on its sources in the supply chain.

Meantime, Citi says expect to see a fifth-generation iPad and a second-generation iPad mini before the year is out. So it could be a busy second half of 2013 for Apple.